Art of molding pulp containers



Dec. 3, 1935. E. HUFF ET'AL ART OF MOLDING PULP CONTAINERS Filed Jan. 9,1933 2 Sheets-Sheet 1 0m: uuuuuummmnnumuunmmu0 I ZSnoentors Z E 85 I W ao (Ittomegs Dec. 3, 1935. E. HUFF ET AL ART OF MOLDING" PULP CONTAINERS2 Sheets-Sheet 2 Filed Jan. 9, 1933 Patented Dec. 3, 1935 PATENT OFFICEART OF MOLDING PULP CONTAMS Ernest Hull, Milwaukee, and Andrew Keiding,Whitefish Bay, Wia, assignors to American Lace Paper Company, Milwaukee,Wis. 1

Application January o, 1933, Serial No. csa'us llll Claim.

This invention relates to improvements in the art of molding pulpcontainers.

As in companion application No. 491,433 filed October 27, 1930, it isthe primary object of the present invention to provide a substantiallyrigid container having a smooth wall both inside and outside, of unusualmechanical strength, unusual resistance to disintegration by hotliquids, unusually low thermal conductivity, and unusually attractive asto the novel appearance in which the wall is finished externally.

The present application is concerned with novel methods by which areceptacle or container of the desired type may be economically,rapidly, and effectively produced complete, the casting, drying, formingand trimming operations being correlated to produce the desired result.

It is a further purpose of the invention to pro-.

vide a process by which material roughly deposited on the usualforaminous form may be manipulated to provide an excess at predeterminedpoints and used to build up embossing without underlay whereby ribs andthe like may be provided either in the inner or outer surface of thereceptacle without any corresponding interior channel. To mold a wall ofvarying cross section in an article otherwise having the smooth surfacedimpervious characteristics above noted, is an objective not'hithertoachieved.

In the drawings: I

Figures 1 to 3 illustrate diagrammatically in vertical section thesuccessive positions of apparatus used in molding the blank from which areceptacle is manufactured in accordance with the present invention.

Figures 4 to '7 represent diagrammatically in vertical axial section thesuccessive positions of apparatus used in the forming of the receptaclefrom the blank.

Figure 8 is a fragmentary detail in vertical section of a compoundsizing and trimming die used in the completion of the receptacle.

: Figure 9 is a fragmentary detail view showing the parts of the die ina plane at right angles to that at which Figure 8 is taken, and indifferent relative positions with reference to each other.

Figure 10 is an enlarged view partially .in side elevation and partiallyin vertical axial section, of a completed receptacle made in accordancewith the invention.

Like parts are identified by the same reference characters throughoutthe several views:

As exemplifying the articles that may be made in accordance with thisinvention, I have illustrated a container or cup preferably molded frompulp on aforaminous body such as that Show at it. In practice theexternal surface of such a body is usually made up of a fine meshscreen, suitably supported from within. For the pur- 5 poses of thepresent invention the said body preferably has its bottom in convex formto provide extra material which may be shaped as shown in Fig. 10.

The pulp blank from which the article is to be 19 formed is cast byconnecting the foraminous body H to a pipe :12 temporarily connected toa source of low pressure. The "assembly is then lowered into a vat 55containing a liquid in which paper or wood pulp or other fibrous pulpmaterial is 15 carried. In. ordinary practice the pulp will contain asocalled size, which is an insoluble solid. Such a. size will give stiiiand rigid body to the pulp arti-v cle if the article is not greatlydisturbed after it dries. H, however, the article is manipulated to anyconsiderable degree after it becomes dry and the size has set, the wallof the article will be comparatively flabby and less impervious thanwould otherwise be the case. It is because of this consideration that itis necessary to shape the pulp while wet to a form in which the cup maybe completed with a of manipulation when dry.

The vacuum to which pipe it? is subject will withdraw the liquid fromtank l5, thereby depositing the pulp content cn the surface of thereticulated mold H in a manner well known to the art. The exteriorsurface of the deposited blank it, as shown in Figs. 2, 3 and 4, wil behighly uneven. When deposited to a substantial thickness, it may bedescribed as lumpy in the sense of such irregularities as occur in arough plaster or stucco. The interior surface of the blank will take theform of the mold II and will show the ill reticulated pattern of thescreen cloth comprising the exposed surface of the mold.

When the blank has been built up to the de-r sired thickness of depositon the mold, the mold is raised from vat 15 as shown in Fig. 2 and theblank and mold are surrounded by a hood H which is lowered to contactwith a plate 18 which covers the top of the vat l5. Into the closedchamber thus formed about the newly deposited pulp, a drying fluid athigh temperature is released from pipe 20 as shown in Fig. 2. This fluidmay comprise steam or, under some conditions, hot air may be used. Ineither case, the effect of the high temperature and the relatively dryfluid upon the wet pulp is such as to result in a fairly rapid butnevertheless incomplete drying of the pulp. During this operation theplate I! prostill very wet, from the mold into the aperture of tray 2|.

Following the treatment with hot drying fluid,

the pulp comprising the blank I! will be in such condition that'it mayimmediately be subjected to a forming operation. About fifty per cent ofits weight will comprise free "water, as distinguished from such wateras will ultimately be retained in its composition. The presence of thisamount of water is very desirable to the successful use of any formingoperation and particularly to those described in the above identifiedcopending' application and to that shown in Figs. 4 to 7 of the drawingsof this application.

If much more than 55 per cent of water by weight is present in the pulp,the pulp will be too soft to be molded properly. If much less than 45per cent of removable water is present in the pulp the fibers will, to avery considerable-extent, be broken during the finishing operation andthey will fail to become properly felted or interlocked. While water isreferred to, in accordance with standard practice, it will be understoodthat the invention is not limited to the use of water as a vehicle forthe pulp.

The wet pulp blank I6 is conveyed by means of tray 2| to a mandrel 23rotatably mounted on support 24 and having peripheral openings 25 (Fig.6) connected by a pipe 26 with a source of low pressure. The withdrawalof air through pipe 26 is indicated by the arrow in each of Figs. 4 t 6inclusive.

The vacuum produced on the peripheral surface of mandrel 23 by means ofthe vacuum line 26 and the apertures 25 does not serve to withdraw waterfrom the pulp blank I, but merely serves to hold the blank to themandrel. It is found that in the absence of some such expedient theblank will not only shift on an internal mandrel during the formingoperation, but will be rolled out or distorted in such a way astoincrease its diameter. This is very objectionable as the manufactureof a container to specific dimensions is one of the commercialrequirements in this art.

With the blank held by vacuum to the rotatable mandrel n as rsiiown. inm. 4, a cup-shaped forming die- 21 provided with gearing 28 for itsmechanical rotation is lowered on to the cup in an offset and inclinedposition with reference to the axis of mandrel 23. The forming die 21has an interior surface 29 which exceeds slightly the diameter of thefinished cup and is preferably perfectly smooth except for channels llwhich may be made in the die to produce ribs in the cup when desired. Atthe lower marginal portion of ulp- As above noted, the Fig. 4 positionof the forming die is such that its axis is laterally offset to theright from the axis of mandrel 28, and is also inclined to the rightwith reference to the mandrel. By virtue of this arrangement the beveledor flared marginal portion SI for the forming die first contacts thepulp about two thirds of the way down the blank and the reaction of thepulp itself serves to overcome the pressure which inclines the formingdie to the right. Thus, as the die moves downwardly over the blank, itis progressively straightened until it is fully, engaged with one sideofthe blank from top to bottom thereof as shown in Pig. 5.

The forming die 21 is rotated as it moves downwardly. The net result ofits rotation and its ofl center and inclined engagement with the blankis to subject the blank to a slight drawing. operation in addition tothe compression which is ultimately effected by the relatively smallclearance between the forming die and the mandrel. It is found that anyexcess of material isgradually worked downwardly toward the margin ofthe blank by this operation and there is no such pulling or tearingaction as tends to destroy the blank if the above described steps areomitted. Furthermore, the excess of material displaced by theprogressive movement of the forming die relative to the mandrel servesto fill the grooves II in .the forming die, thereby creatingcomplementary ribs 34 on the outside of the hardened receptacle. Theieis also a certain amount of surplus material forced to the bead portionI! of the receptacle. I

The requisites of a suitable receptacle are achieved with much greaterperfection by the downward movement of the die in its inclined andoffset position than is possible if the die is 35 moved downwardly in anaxial oifset direction or is moved downwardly in a concentric positionand is later offset.

The clearance between the forming die and the mandrel is very much lessthan the original thickness of the pulp blank as shown in Fig. 2. Theresulting pressure is applied somewhat as if by a rolling operation dueto the movement of the forming die and mandrel about different andmutually oifset axes. There is, moreover, a certain slight amount offriction 'due to the fact that both the mandrel and the forming die areincontact with the wall of the cup throughout its height and the wall istapered as shown.

Because of the fact that the axis of the external die 2'! falls withinthe mandrel or internal die 23 (the axes of the two dies being onlyslightly offset) the eifect upon the pulp blank is wholly difierent fromthat which would be produced if one of the rolling surfacesdeviated'sharply from the other. The pulp is, of course, yieldable andconsequently the pressure is applied throughout a relatively broad zone.In this pressure zone, the external and internal surfaces of the blankare forced to conform to arcuate die surfaces m which are convex inthesame direction and deviate but slightly from each other. Thus there isno sharp fiexing of the fibers, such as would tend to break the fibersand impair the strength of the cup if the compression surfaces were morewidely deviant.

Not only is the forming die preferably grooved, but the mandrel'is alsopreferably shouldered at 81 (Fig. 6). The conformation is such that whenthe cup is molded thereon it will have a complementary internal rib at30 and an annular recess at 3!, as clearly appears in Fig. 10. It isparticularly to be noted both with reference to the external ribs 34 andthe internal rib 38, that the opposed surface of the cup issubstantially smooth, no underlay being required to produce this effectby the present process.

The conformation of the mandrel above described is such that the ribportion 38 of the cup is interlocked with the mandrel when the formingoperation is completed, as shown in Fig. 6. At this point the formingdie 27 is first moved to a position concentric with the mandrel to freeribs 34 from channel 30. It is then lifted from the cup as shown in Fig.'1 and fluid under pressure is now supplied to pipe 28 as indicated bythe arrow in Fig. 7. As a result, it will be found that the cup can beblown from the mandrel without destroying it. If the cup is molded witha proper degree of water-free content within the limits above described,its fibers will be so interlocked and felted and so substantiallyunbroken during the forming operation, that they will have sumcientelasticity to cause the cup to resume its form after being blown fromthe mandrel as above described.

The drying of the cup is now completed, in a kiln or otherwise.

The fully dried cup is now subjected to a sizing and trimming operationin some such die as that shown in Figs. 8 and 9.

Air withdrawn through duct 38 holds the cup to a sizing die as having arelatively large marginal portion 68 conforming to the exact desireddimensions and shape of the rim of the cup.

' The sizing die 39 is yieldable against the pressure the blank-which istrimmed ofi in the shearing operation which forms the margin of the cuprim. Extending transversely beneath the sta tionary shear id is a bridgemember All resiliently supported by compression springs tltjo carry thebottom forming die 69.

In the extreme position of the parts following the shearing operation,as shown in Fig. 9, the cup is forced on to the sizing die :39, theouter shear 62 has moved past the inner shear (l severing the surplusmaterial 36 at the edge of the blank and compressing the elastic ringdid, the

bottom stamp 63 has forced the bottom of the cup against the bottomforming die id which has pressed upwardly the central portion of the cupl as shown at till, the bottom forming die d9 being supported initsretracted position by contact with the base plate 55.

Since there is substantial friction between the cup and the shear die 55which engages the side of the cup, the bottom die l?) serves as'anejector to force the cup out of the inner shear die and allow it'to passupwardly upon the sizing die At the completion of the operation the cupis blown from the sizing die by supplying air under pressure to duct 38in lieu of the vacuum with which such duct was originally incommunication.

In the completed article shown in Fig. 10 the walls will be found to beexceptionally hard and smooth, bearing no evidence of rubbing or thebreaking of nbers and showing no pressure lumps of pulp have beenfiattehedby the pressure exerted during the operation shown in Fig.

process will be found to be uniform in size at and 10 above rib 38 dueto the operation of the sizing dieas above noted. This feature makes itconveniently practicable to use this cup as a container into which adisk shaped cover may be inserted with a snap fit into groove 39 asfrag: mentarily shown at 52 in Fig-10. As above noted, it is unknown ina receptacle of this type and smooth finish, both inside and out, tohave ribbed surfaces without underlay and opposed by perfectly smoothcup surfaces.

v as a result of the particular forming operation above described, allmarks of the mold and all irregularity of surface attributable to thecasting will have been completely eliminated. Additionally, the surplusmaterial required at the bead and at the ribs above described and at thebottom of the cup, will have been supplied in such manner that thecompletion ofthe cup will not have involved any weakening of the cupstructure such as might occur if the mateso rial were subjected undulyto tension in the forming of these parts.

The article produced by the process herein disclosed and claimedcomprises the subject matter of a companion application executed of evendate herewith and entitled Receptacles of molded pulp.

We claim:

l. The process of manufacturing containers from fibrous pulp whichincludes the step of 40 simultaneously drawing and rolling a hollowblank. r

2. The process of manufacturing receptacles from fibrous pulp whichincludes the fixation of a hollow pulp blankupon a correspondinglyshaped mandrel, and the application to the outer surface of the blank ofa drawing and rolling pressure axially and rotatively advancing toact.on successive portions of said blank.

3. The process of manufacturing receptacles from fibrous pulp whichincludes placing a wet pulp blank upon a mandrel and exerting a drawingpressure on rotatively successive peripheral portions of the blank.

4. The process of manufacturingpulp articles which comprises thedeposit-molding of a blank from size-containing pulp stock, thedisplacement of wet pulp from one portion of said blank to anotherportion thereof, the drying of the blank, and the application ofpressure to the I a portion of the material of said wall to build up thethickness thereof, at predetermined points about said wall bothinternally and externally thereof and the pressure manipulation of thebuilt up portions of the wet blank to produce shoulders both internallyand externally thereof. to

receptacle, the pressure forming of the blank 6. The process ofmanufacturing receptacles from pulp which includes the deposit-moldingof a blankin the general form oLthe desired while wet to compact thepulp and displace portions of it toward the margin of the receptacle,the drying of the blank, and the subsequent compression of the marginalportions of the blank upon which such excess of material was deposited.

7. The process of manufacturing a receptacle from pulp which includesthe compression of marginal portions of a pulp blank, and the dietrimming thereof while subject to compression.

8. The process of manufacturing a receptacle of pulp which includes thedisplacement of wet pulp on a wet blank toward the margin thereof, thedrying of the blank, the compression of the marginal portion of theblank, and the trimming therefrom of the surplus material.

9. The process of manufacturing a receptacle from pulp which includes arolling operation in aoaasoo which a hollow pulp blank is compressedtoward its center in axially extending zones successively oflset in aperipheral direction, the pressure in each zone being applied to thebiank'in a man-' ner to require corresponding inner and outer surfacesthereof to conform to'slightly deviating arcs whereby the blank isrolled without subjecting its fibers to sharp bending strains.

10. The process of manufacturing receptacles of pulp which includes thesuccessive compression of successive peripheral zones of a wet pulpblank into conformity with arcs deviating but slightly fromconoentricity, axially extending the successive zones of pressure toinclude increasing areas of the blank, simultaneously displacing aportion of the material thereof, and shouldering both internally andexternally of said blank the portion thereof toward which said materialis displaced.

mas-r HUFF. ANDREW xnmma.

